Plaster spray gun



May 29, 1951 J, McNULTY ETAL 2,555,238

PLASTER SPRAY un Filed June '7, 1949 2 Sheets-Sheet 1 inventors Jasgph m. mcnqlg J. M. M NULTY El AL May 29, 1951 PLASTER SPRAY GUN 2 Sheets-Sheet 2 Filed June 7, 1949 Ina/en tars Jos h m mchqliq Patented May 29, 1951 PLASTER SPRAY GUN Joseph M. McNulty, Hinsdale, and Andi Schiltz, Elburn, Ill., assignors, by mesne assignments, to E-Z-On Corporatiomflhicago, 111., a corporation of Illinois Application June 7, 1949, Serial No. 97,660

'7 Claims. 1

This invention relates to a method of and means for plastering surfaces such as ceilings, walls, etc., by projecting the plaster onto the surface. It is one of the objects of the present invention to provide a method of and means for spray type plastering wherein the plaster may be built up to its desired thickness and wherein the exposed surface will be a smooth; substantially flat surface. The built up thickness may be quite substantial, and may exceed a major fractional part of an inch or may even be an inch or more.

It has heretofore been proposed to plaster a wall surface by spraying a plaster mix against the surface. Insofar as we are aware, one of the insurmountable difficulties with the plaster spraying as suggested in the past has been that the resulting wall surface would have ridges.

To the best of our knowledge it was extremely difficult heretofore to build up a substantial thickness of plaster on a surface by the spray process and end with a smooth surface devoid of ridges or undulations. It is an object of the present invention to provide a method of plaster spraying which will substantially overcome the above mentioned difiiculty. In accordance with the principles of the present invention there is provided a plaster spray gun of the type adapted to project a plaster mix with a column of air under pressure wherein the distribution of the mix and the air at the nozzle exit is such that when the stream of the mix emitted from the nozzle is moved across a wall surface the material will be deposited on the wall to a substantially uniform thickness.

In the past the nozzles of plaster spray guns have been provided with a throat for imparting direction to the stream of material emitted therefrom. There would necessarily be some friction between the flowing plaster mix and the wall surface of the long throat so that the velocity of flow would necessarily be somewhat smaller at the periphery of the flowing mass where it is retarded by the throat of the orifice than at the center of the orifice. The net effect of such movement was that more material would be emitted per unit of time at the center of the orifice than at the rim thereof so that the plaster would tend to build up in mound formation at the portions of the wall where the center of the flowing stream impinges. This tended to produce on the plaster wall a pattern of moveof the spray gun as the wall was being sprayed. Furthermore, the projection of the stream of plaster onto the wan is generally a circle. If that circle is of uniform thickness and is then moved. across the surface being plastered the resulting locus of the circle will be a band of a width equal to the diameter of the circle, and of a thickness which is maximum at the center of the band and tapers to a minimum at the edges of the band. In sprayed plaster walls this is the ridge formation which is so highly objectionable. In order to eliminate the formation of visible ridges it is necessary to cut down the amount of plaster material that is deposited at the center of the band above referred to and to increase the amount of material that is deposited at the edges of the band above referred to. We have discovered that the circular stream of plaster material that is projected against the wall and then moved along the wall must not be thicker at the center as was generally the prior practice. Also; it must not be of uniform thickness. The circular plaster ring that is projected against the wall must be of maximum thickness adjacent its rim and of minimum thickness at its center so that when such a circle of plaster being projected from a spray gun is moved across the wall the resulting deposit of plaster onto the wall will produce a plaster band approaching uniform thickness.

In order to accomplish the above results with a plaster spray gun it is necessary that the fiow' of material through the orifice shall be substantially unretarded at the periphery and it is necessary also that there shall be less material at the center than at the rim of the stream so that the thickness of the material deposited. on the wall, if the spray gun were held stationary, would be less at the center than at the rim of the circle of plaster thus deposited on the wall.

In order to accomplish the above results we provide a plaster projecting nozzle having .an orifice with a throat of minimum thickness, say, of the order of a throat thickness of one-eighth the orifice diameter. An air tube projects a stream of air under pressure centrally through the plaster emitting orifice. The air tube preferably terminates close to the plaster emitting orifice but on the upstream side thereof. The air emitting tube is of a diameter approximately two-thirds the diameter of the plaster emitting orifice. As a result of this arrangement the material leaves the orifice as a stream comprising a central core of air under pressure surrounded by an outer layer of plaster mix, The expansion of the central core of moving air tends to force the material of the plaster mix outwardly. This in combination with the fact that the throat of the orifice is of a minimum thickness and therefore offers a minimum restriction to the fiow of the plaster mix results in a tendency to increase the concentration of plaster material at the periphery of the flowing stream in comparison with the concentration of the material towards the center of the flowing stream. We have found that when such a stream of plaster material and air is moved across a wall surface in the act of spraying plaster the resulting plaster surface may readily be built up to its desired thickness without the production of ridges, corrugations or pattern lines.

It is a further object of the present invention to provide a plaster spray gun wherein the plaster is forced through the nozzle orifice by pressure applied to the plaster and wherein the air flowing through the orifice is not intended for drawing plaster through the orifice and is not intended primarily to be mixed with the plaster leaving the orifice. In the preferred embodiment of the present invention the air tube is of a substantially smaller size than the size of the orifice of the nozzle, so that the air from the tube is projected through the orifice as a divergent stream which at the orifice has not reached the diameter of the orifice, so that the air stream does not to any major extent touch the edge of the orifice. Instead the air stream moves within the stream of plaster flowing through the orifice. As the air tube is moved slightly further away from the upstream side of the orifice the effective diameter of the air stream at the orifice is increased, thereby increasing the diameter of the core of air flowing through the orifice and correspondingly increasing the width of the rim of plaster of said stream. Such adjustment to some measure controls the angle of divergence of the stream of plaster emitted from the orifice. All this is due essentially to the fact that there is substantially no mixing of air and plaster at the orifice due to the fact that the orifice has substantially no throat.

It is a further object of the present invention to provide a plaster type spray gun which is so constructed that the nozzle may be easily removed and replaced as may be necessary for cleaning purposes or for replacing by a nozzle of a different construction.

It is a still further object of the present in vention to provide a plaster spray gun which is so constructed that the position of the air pressure tube within the gun may be readily shifted to adjusted locations and then locked in position of adjustment required either by the fluidity of the mix or by the nature of the job that is to be done.

It is a still further object of the present invention to provide an arrangement wherein there is a simple and convenient means for sealing the spray gun against leakage of plaster at the interifitting surfaces between the spray gun and the slidable air tube thereof.

It is a till further object of the present invention to provide a method of spraying plaster wherein the plaster mix is fed into the spray gun continuously, as distinguished from the intermittent or pulsating pressure arrangements of the past. When the plaster mix is fed to the spray gun by means of a reciprocating or pulsating type of pump the pulsations in the fiow of plaster are contributing factors that accentuate the formation of undulations in the plaster wall surface. By the present invention the plaster is fed to the spray gun at a uniform 4 non-pulsating pressure. In accordance with the preferred embodiment of the present invention the plaster is fed to the spray gun by a plaster pumping apparatus known as a Moineau pump.

The attainment of the above and further objects of the present invention will be apparent from the following specification taken in conjunction with the accompanying drawings forming a part thereof.

In the drawings:

Figure 1 is a side View of a plaster gun embodying the present invention;

Figure 2 is an end view thereof;

Figure 3 is a sectional view taken along the line 3--3 of Figure l and looking in the direction of the arrows;

Figure 4 is a sectional view taken along the line 4-4 of Figure 2 and looking in the direction of the arrows;

Figure 5 is a view taken along the line 5-5 of Figure 1 and looking in the direction of the arrows; and

Figure 6 is a perspective view of an air adjustment pusher of the plaster gun.

Reference may now be had more particularly to the drawings wherein like reference numerals designate like parts throughout.

At I there is shown a plaster spray gun embodying the present invention. The gun includes a body 2 which is preferably a smooth metal casting having a downwardly extending portion 3 adapted to be gripped by the hand and terminating at its upper end in a horizontally directed nozzle-receiving discharge portion 4. At its lower end of the downwardly extending portion 3 has a threaded pipe nipple 5 for receiving a fitting 6 to connect to a hose that supplies a plaster mix under pressure to the spray gun. The body 2 also has a bushing-receiving projection 8 in which is mounted a bushing 9 that is coaxial with the center of the discharge portion 4. The bushing 9 may be press fitted into the projection 8. An air tube I2 is slidable through the bushing 9. A ring gasket I3 is provided in the bushing 9 for making a sealing fit with the air tube I2 and thus prevent the seepage of material from within the spray gun through the space between the air tube I2 and the bushing 9. An air adjustment pusher M is slidable on the air tube 12 between the body 2 of the spray gun and a fitting [5 that is secured to the end of the air tube l2 and is adapted to receive an air line nipple l6 at the end of an air pressure hose IT. The fitting l5 has a peripheral groove 49 forming a flange 2|. The groove [9 is adapted to receive the nose portions of a pair of spring clips 2222 that are secured to the pusher M in any desired manner, thereby permitting an easy attachment or detachment of the fitting I5 and the air adjustment pusher l4. The air adjustment pusher i4 is adapted to be moved back and forth by a U-shaped air adjustment lever 24 that has an operating knob 25 secured to one end thereof and the arms of which lever embrace the pusher M and are pivoted to the body 2 by an air adjustment pivot pin 26 that extends through an enlargement 21 on the outside of the body 2 and is locked in place by a screw 28. The pivot pin 26 passes through eyes at the bottoms of the arms of the air adjustment lever 26. The pin 2 is threaded at one end and has an air adjustment lock lever 3| threaded thereon for forcing the bottom of the two arms into pressure engagement with the enlargement 21 to lock the arms 24 in their angularly adjusted positions. The arms 24 have a pair of trunnion 'pins 33threaded therethrough,the ends of which portion there is located a nozzle 4|. This nozzle is of a generally cylindrical outsideshape and fits snugly within the discharge portion 4 of the spray gun and has a peripheral flange 42 that fits against the end of the dischargeportion- 4. A pair of sprin clips 43 are secured to the discharge portion 4 of the spray gun and hold the nozzle-in place.

If the clips are flexed outwardly the nozzle may be readily removed from the spray gun as may be necessary for cleaning or replacement.

' The nozzle has an orifice 44 which has substantially a knife edge. The downstream side 45 of the orifice is at substantially right angles to the center line Mi, which is the axis of the stream of fluid that flows through the orifice. The upstreamor approach side 4'! of the orifice is of a generally conical shape the elements of which are at an angle substantially less than 90 to the axis of flow 46;which is also the axis of the surface 47. It is to be noted that the axis of the cone formed on the approach 4'! is on the center line 46 and at a point past the down stream side of the orifice. The orifice 34 is substantially a knife edge orifice so that there is substantially no throat or that the throat, if any, is of a minimum length consistent with the maintenance of the diameter of the orifice and the internal diameter of the air tube l2. Dueto this smallness of the axial length of the orifice, the air flowing from the tube I2 does not have much of an opportunity to expand as it flows through the orifice but must do substantially all of its expanding after it leaves the orifice and is in the open atmosphere. This expanding forward moving air stream acts on the plaster emitted from the apparatus'to change it from what would be a stream of plaster to a spray of plaster.

The portion 4 of the body of the plaster spray gun has a pair of parallel plate-like flanges |5 I projecting from one side thereof. Between these flanges there is mounted an electric switch 52.

This switch is connected in electric circuit with the'motor that operates the pump that forces the plaster into the plaster spray gun and with the machine that supplies the air pressure. Thus, by turning off the electric switch at the spray gun the flow of air and of plaster to the gun is stopped.

' eter appreciably less than the diameter of the orifice 46', and the longitudinal axis of the tube l2 is coincident with the axis &6 of the orifice. The

tube' It. may be adjusted longitudinally towards andfrom the orifice M. During operation of the square inch.

spray gun a plaster mix is fed to the gun byv a pump that operates with a continuous fixed pressure, as distinguished from the reciprocating or pulsating pumps. As the steam of plasteris being forced through the orifice 44 by the pressure that is applied thereto by the plaster feeding pump there is also being directed a stream of air through the air tube 12, which stream of air also flows through the orifice. The air is under pressure which may equal or even exceed the pressure of the plaster mix. It is desirable that the air pressure shall not exceed the pressure of the material by more than a few pounds per As'the air leaves the tube l2 it issues as a stream that immediately commences to diverge or increases in diameter as its distance from the open end of the tube i2 increases. The

velocity of air flow and the spacing of the end of the air tube l2 are such that the air stream has not expanded to the diameter of the orifice 4% as it passes through the orifice. Therefore the air stream does not engage the periphery of the orifice but forms a core through the stream of plaster that is flowing through the orifice. The plaster mix is therefore in the form of a ring of an external diameter fixed by the orifice and of an internal diameter determined by the air stream, which in turn iscontrolled by a number of factors one of which is the adjusted position of the open end of the air tube 52 with respect to the knife edge of the orifice. As the open end of the tube i2 is brought closer to the orifice the diameter of the air stream at the orifice approaches the inside diameter of the tube 12, whereas as the tube 12' is retracted from the orifice the diameter of the air stream at the orifice increases. When the stream of air and plaster leaves the orifice the expanding air stream tends to force the plaster mix in a direction outwardly of the center of the stream so that as aresult, at a distance from the spray gun there is a minimum-of plaster flow at the center of the stream and a progressive increase in the amount of plaster flowing at the periphery of the stream. This is possible only because there is no substantial mixing of air withthe plaster in the nozzle. This stream of air and plaster is projected against a wall surface that is to be plastered. If the stream were held at one position on the wall it would tend to build up a ring of plasterthinner at the center and progressively thicker towards the periphery. However, the stream of plaster is not held in one position against the wall. It is moved across the wall. As it moves across the wall it builds up a layer of plaster which can be made of substantially uniform thickness Without the ridges that were heretofore characteristic of sprayed plaster walls. In order to assure a non-ridge formation of the plaster as it is built up it is firstv desirable to make a test plastering run. If a ridge is formed on the test run then the air tube is adjusted towards or from the orifice and another test run is performed. The bestposition ofthe end of the air tube withrespect toithe orifice is determined by the consistency of the plaster mix that is being projected and by the relative air and plaster pressures.

Plaster used with thepresent spray gun is preferably an expanded Perlite aggregate and ceinentwhichmay be of a consistency usually the delivery from which is non pulsating, for in- 26 stance, apump such. asyshown in the patent .to

Moineau, No. 2,028,407. The pressure of the plaster mix flowing to the spray gun may be controlled in any manner known in the art. This pressure is entirely independent of and in no way affected by the pressure of the air flowing through the tube I2. The plaster mix that is supplied to the spray gun contains a sufficient amount of entrained air to make the mix compressible.

When it is desired to clean the spray gun it is a very easy matter to disassemble the same. The nozzle-holding clips 43 are sprung outwardly manually. This permits removal of the nozzle 4| from the spray gun. By springing the clips 22 outwardly it is possible to retract the air tube I2 from the spray gun. This may be done even while the air adjustment pusher i4 and the air adjustment lever 26 remain locked in their previously adjusted position. As a result the reassembly of the air tube in the spray gun does not require a resetting of the air adjustment lever. In accordance with the present invention the air pressure used is sufficiently low that with the spray gun at the required distance from the surface being sprayed the air fiow will cause no blasting or abrading effect on the surface. Substantially all of the velocity of the air will have been spent before the air reaches the surface to which the plaster is being applied. It is within the concept of the present invention to use the spray gun close enough to the plastering surface that the velocity of the air striking the surface or the plaster newly sprayed thereon is sufiicient to exert a mild smoothing effect on the newly sprayed plastic plaster as the stream of air and plaster is moved across the surface.

The air pressure used is low enough and sufiiciently proportionate to the pressure of the material being sprayed so that the gun can be used as close as two or three inches from the surface being plastered without causing a substantial identation in the plaster. Therefore the gun is equally useful in the application of screeds or in plastering narrow spaces and in plastering walls where it may be held three or more feet from the surface being plastered.

In compliance with the requirements of the patent statutes we have here shown and described a preferred embodiment of our invention. It is, however, to be understood that the invention is not limited to the precise construction here shown, the same being merely illustrative of the principles of the invention. What we consider new and desire to secure by Letters Patent is:

l. Plaster spraying apparatus comprising a nozzle the downstream side of which is open directly to the atmosphere and makes a larger angle with the axis of flow than does the upstream side and both sides of which meet at the orifice opening in a dull knife edge forming a throat of an extent less than one-fourth the diameter of the orifice of the nozzle, and an air line having an opening on the upstream side of the orifice directed towards the orifice on an axis coincident with the axis of flow through the orifice.

2. Plaster spraying apparatus comprising a nozzle the downstream side of which is open directly to the atmosphere and makes a larger angle with the axis of fiow than does the upstream side and both sides of which meet at the orifice opening in a dull knife edge forming a throat of an extent less than one-fourth the diameter of the orifice of the nozzle, and an air line having an opening on the upstream side of ell) the orifice directed towards the orifice on an axis coincident with the axis of flow through the orifice, the orifice being of a diameter larger than the opening in the air line, and means for moving the air line towards and from the orifice to vary the diameter of the air stream at the orifice; said means comprising a hand operated lever pivotally mounted on the spraying apparatus for swinging movement towards and from the nozzle, means for releasably securing the air line to the lever, and means for releasably locking the lever in adjusted position.

3. A plaster spray gun having a spray nozzle with a knife edge orifice therethrough, the downstream side of the orifice being at substantially to the axis of flow through the orifice and the upstream side of the orifice being a portion of the surface of a cone whose central axis is coincident with the axis of flow through the orifice and whose apex is located outside of and on the down stream side of the orifice.

4. A plaster spray gun having a spray nozzle with a knife edge orifice therethrough, the downstream side of the orifice being at substantially 90 to the axis of fiow through the orifice and the upstream side of the orifice being ata smaller angle to the axis of fiow through the orifice and at such an angle to the axis of flow as would result in intersection with the axis of fiow outside of and past the down stream side of the orifice, means for directing a stream of plaster to and through the orifice, and. means including an air tube for directing a stream of air centrally through the plaster flowing through the orifice, the length of the orifice in the direction of fiow therethrough being less than the difference between the diameter of the orifice and the inside diameter of the air tube.

5. A plaster spray gun having a spray nozzle with a knife edge orifice therethrough, the downstream side of the orifice being at substantially 90 to the axis of fiow through the orifice and the upstream side of the orifice being a portion of the surface of a cone whose central axis is coincident with the axis of flow through the orifice and whose apex is located outside of and on the down stream side of the orifice, means for directing a stream of plaster to and through the orifice, and means for directing a stream of air centrally through the plaster flowing through the orifice, said last named means comprising an air tube having an opening that faces the upstream side of the orifice and is centered on the orifice center, the inside diameter of the tube being less than the diameter of the orifice, and means for shifting the position of the open end of the air tube towards and from the orifice.

6. A plaster spray gun having a spray nozzle with a knife edge orifice therethrough, the downstream side of the orifice being inclined to the axis of flow through the orifice and the angle of inclination being such as would result in intersection with the axis of fiow outside of and past the downstream side of the orifice, means for directing a stream of plaster to and through the orifice, and means for directing a stream of air centrally through the plaster flowing through the orifice, said last named means comprising an air tube having an opening that faces the upstream side of the orifice and is centered on the orifice center, the outside diameter of the tube being less than the diameter of the orifice, the

length of the orifice in the direction of flow therethrough being less than the difference between the diameter of the orifice and the inside diameter of the air tube, and means for shifting the position of the open end of the air tube towards and from the orifice.

'7. A plaster spray gun having a spray nozzle with a knife edge orifice therethrough, the downstream side of the orifice being at substantially 90 to the axis of fiow through the orifice and the upstream side of the orifice being at a smaller angle to the axis of fiow through the orifice, means for directing a stream of plaster to and through the orifice, an air tube having an opening that faces the upstream side of the orifice and is centered on the orifice center, inside diameter of the tube being less than the diameter of the orifice, for directing a stream of air centrally through the plaster flowing through the orifice, means for shifting the positions of the open end of the air tube toward-s and from the orifice comprising a handle, a bush REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,751,343 Mack Mar. 18, 1930 1,863,924 Dunn June 21, 1932 2,259,215 Scheurer Oct. 14, 19%1 2,305,269 Moreland Dec. 15, 1942 2,504,805 Clipson Apr. 18, 1950 

